In this work, the phase evolution during calcinations of a BaTiO3 and TiO2 mixture was investigated. Based on the observations, a model for the reaction sequence of the phases was proposed and a modified process was suggested, namely to synthesize Ba2Ti9O20 materials utilizing a BaTi4O9 and BaTi5O11 mixture, instead of a BaTiO3 and TiO2 mixture, as starting materials. The phase transformation kinetics is thus greatly enhanced by this process. While the reaction of the 2BaTiO3+7TiO2 mixture requires 1100 °C/4 h to transform completely into the Ba2Ti9O20 Hollandite-like phase, it needs only 1000 °C/4 h to fulfil the phase transformation process in the BaTi5O11+BaTi4O9 mixture. The BaTi5O11+BaTi4O9 mixture also leads to higher sinterability and more uniform granular structure, as compared to the 2BaTiO3+7TiO2 mixture, when these powder mixtures were densified by a direct sintering process. Furthermore, local microwave dielectric properties measured by an evanescent microwave probe (EMP) reveals that the grains of Ba2Ti9O20 materials prepared from the BaTi5O11+BaTi4O9 mixture possess larger dielectric constant than 2BaTiO3+7TiO2 derived ones, indicating that the BaTi5O11+BaTi4O9 mixture has higher reactivity for the formation of the Ba2Ti9O20 Hollandite-like phase.
